The invention concerns a process for the production of a sealed container comprising a plastic or paper jacket closed off at both ends by plastic closure pieces, one of which pieces contain a tear-off tab.
A container of this type and process for its production are known from German DE-OS No. 30 23 835. The cylindrical jacket is coated at least on the inside with a plastic coating. One of the closure pieces serves as a lid and is provided with an outlet opening and a tear-off tab closing the outlet opening. One of the closure pieces contains a cylindrical projection which is pressed into the jacket and welded or otherwise sealed to the jacket.
In the cylindrical jacket made of coated paper, a disk shaped bottom is attached to an inward flanging of the lower edge of the container jacket, and a similarly disk-shaped lid is attached to the top of the jacket by flanging its outer edge around the top edge of the jacket. The lid is provided with an opening, as known for example from containers for fruit juice or milk beverages, which initially is closed tightly by a sealed tear-off tab. After the tab is torn off, the contents of the container become accessible and may be poured out or removed by the insertion of a straw.
Containers of that type have the disadvantage of a relatively low stability. Another disadvantage is that if the lid contains an extension to be pushed tightly into the container jacket by means of sealing jaws under the effect of heat, the venting of displaced air from the jacket becomes difficult.
It is known (see European Document No. 02 08 352-A1) that a container whose contents are to be subjected later to a heat treatment (for example to be sterilized) may be provided with a bellows-like center part which undergoes thermal expansions together with the air in the container. It is also known from this prior art to provide an opening in the center of the bellows-like projection. That opening is closed by a drop of plastic, which is still liquid at the temperature of the heat treatment and which solidifies only upon the cooling of the container. This expedient is intended to ensure that the volume of air increased by the heating phase is able to leave through the opening. Subsequently, the deformable center part equalizes the temperature. For closed containers of the type containing an outlet opening with a tear-off tab, such a lid is not feasible. In those containers the tear-off tab must as a rule be tightly sealed prior to the application of the lid, as otherwise it is not possible to thereafter join the tear-off tab tightly enough to the lid under the effect of heat and pressure due to a lack of strength of the lid.
An object of the present invention is to eliminate the disadvantage that the air cannot escape from containers of this type during the installation of the closure pieces.